The present invention relates to a process for the treatment of a gas by Temperature Swing Adsorption (TSA), of the type in which each bed of adsorbent is subjected to a cycle which comprises, in succession: an adsorption phase which itself comprises an adsorption step at a low adsorption temperature; an adsorbent regeneration phase which itself comprises a depressurization step; a heating/elution step, during which the bed is purged with a hot heating/elution gas, and a cooling/elution step, during which the bed is purged with a cold cooling/elution gas; and a repressurization phase.
The invention applies in particular to the purification of atmospheric air intended to be distilled, especially by stripping out the water and the carbon dioxide.
The adsorbents used may be activated alumina, doped alumina, zeolites (A, X, LSX, etc.), silica gel or a succession of several of these products.
Adsorption of CO2, water and other impurities is promoted by low temperatures. It is therefore important for the adsorption to be carried out at low temperature and, consequently, the operation universally adopted involves cooling the entire adsorbent down to approximately the low adsorption temperature, which is close to the temperature of the gas to be treated, before starting the next adsorption phase. This way of carrying out the process also has the advantage, in the case of a cryogenic plant located downstream, of minimizing the heat flux sent into this plant when the bed is switched to the adsorption phase.
The object of the invention is to make it possible to reduce the investment and/or to increase the productivity of the plant located downstream, while maintaining satisfactory adsorption performance.
For this purpose, the subject of the invention is a treatment process of the aforementioned type, characterized in that the cooling/elution step is terminated while the cooling/elution gas leaving the bed is at a markedly higher temperature than the temperature of the gas to be treated and in that the adsorption phase comprises an initial adsorption step during which the bed is cooled down to the low adsorption temperature due to the effect of the gas to be treated.
The process according to the invention may include one or more of the following characteristics:
the cooling/elution step is terminated when the cooling/elution gas leaving the bed is at a temperature at least 30xc2x0 C. greater, preferably at least 50xc2x0 C. greater, than the temperature of the gas to be treated;
during at least a first part of the initial adsorption step, the bed is connected up in parallel with another bed at the end of the adsorption phase and the two gas streams coming from these two beds are combined.